Google might have built its success on ads on the Web, but soon enough, the company could be delivering ads to your refrigerators, car dashboards, and even thermostats.

Google wrote a letter to the Securities and Exchange Commission (SEC) in December that the government organization published on Tuesday, saying that while the US government wants to see revenue figures broken out in the mobile ad space, it doesn't make sense because the term "mobile" is ever-evolving. Google was also suspect of breaking out ad sales on "smart devices," since that, too, is subject to change.

"For example, a few years from now, we and other companies could be serving ads and other content on refrigerators, car dashboards, thermostats, glasses, and watches, to name just a few possibilities," Google wrote.

The technologies Google included might not surprise those that have closely followed the company's moves. Over the last several months. Google has an alliance with several car makers, including Audi and General Motors, to bring Audi to vehicles, and the company has acquired thermostat-maker Nest. Its Google Glass eyewear seems like an ideal option to place ads eventually, and Google has modified Android to make it more smartwatch-friendly.

Google didn't guarantee that ads would be coming to the growing list of smart devices, but the company made clear in its letter to the SEC that it sees a future in which ads will be served at precisely the right time, based on need and relevancy.

"Enhanced Campaigns allows our advertisers to write one ad campaign, which we serve dynamically to the right user at the right time on whatever device makes the most sense," Google wrote. "Because users will increasingly view ads and make purchase decisions on and across multiple devices, our view of revenue is similarly device-agnostic."

Despite mentioning thermostats in its letter to the SEC, a Google spokesperson told CNET in an e-mailed statement that the letter "does not reflect Google's product roadmap." The company specifically targeted Nest in its statement, saying what the thermostat-maker "does not have an ads-based model and has never had any such plans."